1. Field of the Invention
The present invention relates generally to a formed ligneous body, and a method of producing the same, and more particularly to a formed ligneous body having a desired three-dimensional shape, and a method which permits advantageous production of the formed ligneous body.
2. Description of Related Art
There have been widely used formed ligneous bodies formed of various kinds of lumber (timber) and bamboo, as components of architectural floor panels, furniture and fittings. Further, there has been a growing demand for interior parts of automotive vehicles having the texture or appearance of wood, keeping pace with a recently increased desire for enhancement of quality of the vehicles. To meet this growing demand, formed ligneous bodies have been increasingly utilized as outer panels and surface panels of the interior parts of the automotive vehicles.
By the way, various kinds of formed ligneous bodies are available. For example, the known formed ligneous bodies are produced by extrusion or pressing of a mixture of a ligneous material in the form of a particulate mass or chips of lumber or bamboo and a thermoplastic resin material, or by insert injection molding using a sliced veneer as an insert, so that the formed ligneous body consists of the sliced veneer as a surface layer portion, and a base layer of a resin material integral with the surface layer portion. These formed ligneous bodies produced by the above-indicated extrusion, pressing and insert injection molding are advantageous for easier production. However, those formed ligneous bodies, which include a large amount of a resinous material, are not considered preferable from the standpoint of preservation of resources and environments, and suffer from a disadvantage in terms of aesthetic dignity and texture as compared with those of a genuine lumber body. The ligneous properties of the formed ligneous body produced by the insert injection molding using the sliced veneer are further deteriorated in the presence of a coating layer (topcoat layer) in the form of a transparent film, which is provided to cover the sliced veneer, for the purpose of improving scratch- or flaw-, water- and weather-proof properties of the surface layer of the sliced veneer.
In view of the prior art described above, Japanese Patent No. 4502848 and Japanese Patent No. 4849609 disclose a formed ligneous body produced by utilizing a so-called “flow molding” process, and a method of producing such a formed ligneous body. According to the flow molding process disclosed in the above-identified publications, a ligneous material is accommodated in a forming cavity formed in a mold, and is heated and pressed to apply shearing forces to fiber cells (cellulose) which are dead cells constituting a fibrous structure of the ligneous material, so that the relative positions of the fiber cells are changed to cause the ligneous material to flow so as to fill the forming cavity with the ligneous material, and so that the ligneous material filling the forming cavity is compressed into a shape following the shape of the forming cavity, whereby the formed ligneous body having the desired shape is produced. Prior to this flow molding operation, a pretreatment is conducted to cut hydrogen bonds among the fiber cells of the ligneous material. For instance, this pretreatment is conducted to control a water content of the ligneous material to a desired value, or to impregnate the wall structure of the fiber cells with a resin material, for example, so that water molecules and molecules of the resin material are adsorbed among molecular chains of the fiber cells cross-linked by the hydrogen bonds, with a result of cutting of the hydrogen bonds among the fiber cells.
Unlike conventional formed ligneous bodies produced by using the prior art ligneous material and resin material, the formed ligneous body produced by utilizing the flow molding process described above does not use a resin material at all, or requires the use of a resin material by only an extremely small amount. Accordingly, the flow molding process has not only an advantage regarding the preservation of resources and environment, but also an advantage of presenting a genuine lumber feel. Further, the formed ligneous body produced by using the ligneous material the fiber cells of which are impregnated with a resin material has an advantage of high degrees of the scratch-, water-, and weather-proof properties of its surface portion, even where the surface portion is not covered by the coating layer in the form of the transparent film.
However, the formed ligneous body produced by utilizing the flow molding process having the several advantages suffers from the following drawback. Namely, the flow of the entirety of the ligneous material within the forming cavity undesirably causes a high risk that the formed ligneous body has surface patterns or figures which are far different from, or deformed with respect to a natural wood grain, or aesthetically deteriorated. Thus, the technique to produce the formed ligneous body by utilizing the conventional flow molding process has extreme difficulty to obtain the formed ligneous body having a decorative design surface with a natural and fine woody grain in at least a portion of its surface.